wscript: Add compiler flag to disable extra warning from Travis.

Older version of GCC generates an extraneous warning about clobbering
variables in tj_array test.
wscript: Add additional flag to valgrind when running tests.
test-tj_solibrary: Remove unused include.
test-tj_solibrary: Use libm instead of libc for unit test.

Ubuntu puts libc.so in a weird spot (at least on 12.04 LTS).  This way,
I don't have to link to a specific version too.